Having a harder time with Penguin.. because my ideas keep going back to Arkham City Oswald (where I feel he was brilliantly executed) -- so having a harder time.

You could just have him be one of the rich people that is still suffering the repercussions of being sacked during Bane's takeover of Gotham. He would still have the whole "lost fortune" back story but reinterpreted it for the Nolanverse.